The microminiaturization of electronic components has created widespread growth in the use of portable electronic devices such as cellular phones, pagers, video cameras, facsimile machines, portable stereophonic equipment, personal organizers and personal computers. As a result, the demand of improved power sources for these devices has been increased. Moreover, telecommunication backup batteries, hybrid electric vehicles, and electric vehicles also require advanced battery materials to meet the high demand and performance. Preferably, the battery materials are environmentally benign and relatively low cost to make these expanded battery applications practical. Relevant batteries include primary batteries, i.e., batteries designed for use through a single charging cycle, and secondary batteries, i.e., batteries designed to be rechargeable. Some batteries designed essentially as primary batteries may be rechargeable to some extent.
Batteries based on lithium have been the subject of considerable development effort and are being sold commercially Lithium-based batteries have become commercially successful due to their relatively high energy density. Lithium-based batteries generally use electrolytes containing lithium ions. The negative electrodes for these batteries can include lithium metal or alloy (lithium batteries), or compositions that intercalate lithium (lithium ion batteries). Preferred electroactive materials for incorporation into the positive electrodes are compositions that intercalate lithium. For example, metal phosphates are candidates for the production of cathode materials that intercalate lithium.
An example of lithium-ion battery is the lithium ferrophosphate (LiFePO4, or LFP) battery, in which LiFePO4 is used as the cathode material LFP exhibits some advantages such as low cost, non-toxicity, natural abundance, excellent thermal stability, safely characteristics, electrochemical performance, and specific capacity (170 mA·h/g, or 610 C/g). As such, LFP battery is even finding a number of roles in vehicle use and backup power, among others. However, LFP batteries are still expensive to produce. For instance, in order to manufacture LFP active material and its dopant, one major production method is using iron oxalate as Fe source precursor and NH4H2PO4 as PO4 source or P source precursor. The drawback is that the manufacturing process for iron oxalate and NH4H2PO4 generates hazardous gas, and the processing cost is very high. Another method is the use of fine quality iron phosphate as precursor for both Fe and PO4 source. However, the manufacturing cost for iron phosphate is also very high.
Another concern associated with traditional methods is the disposing of phosphorous material, which is strictly regulated by the environmental protection agency in all countries.
Factors under consideration for LiFePO4 synthesis include carbon coating, particle size minimization and/or metal tons doping for the purpose of improving the performances of cathode materials in terms of energy density, power density (rate capability), cycle life (stability). Regarding particle size minimization, nanosize carbon coated LiFePO4 cathode materials display very excellent electrochemistry properties. Nanosize LiFePO4 particles with micron/nanostructures are highly desired for designing high-performance lithium-ion batteries with high volumetric energy density and good rate capability. These structured LiFePO4/C particles create 3D electronic and ionic pathways, which facilitate electron migration in the solid phase and lithium ion diffusion in the liquid phase and provide the material excellent cyclability and superior rate capability. These micron/submicron-sized LiFePO4 well-structured particles have a high tap density and, as electrodes, show excellent rate capability and cycle stability.
Thus, there exists not only a need of new method or process that can produce LFP and FePO4 at a lower cost and in a more environmentally friendly way, but also a need of simpler and more cost-effective method for preparing nanosize LiFePO4 particles. Advantageously, the present invention provides a novel method of synthesizing a phosphate salt that can meet these needs.